centos syslog is slow on Dell server

We have 1950 Poweredge server running on CentOS for asterisk and calling card purpose, but the server is extremely slow when there are many logs (like 20 or 50 logs per second) sent to syslog and it will take 5 times slower than a normal PC, though the server has latest 2.5Ghz with two CPU and each quad core and 4GB of 1333MHz Memory.